Field of the Invention
The present disclosure relates to a method for controlling a plurality of parallel-connected invertors.
Description of Related Art
Generally, an inverter drives a motor by converting an AC (Alternating Current) power source into a DC (Direct Current) power source, and successively, outputting an AC voltage after switching the DC power source using switching elements such as IGBTs (Insulated Gate Bipolar Transistors) under control by a PWM (Pulse Width Modulation) signal inputted from a controller.
That is to say, an inverter is a machine configured to effectively control a motor, and therefore is designed to reduce power consumption of the motor and increase energy efficiency.
Meanwhile, in order to drive a large capacity motor, a large capacity inverter is also required. However, it is difficult to produce a large inverter because there are still existing limits in developing inverter's essential component such as IGBTs (Insulated Gate Bipolar Transistors) and diodes. Therefore, a large capacity motor is driven in a synchronous operation using a plurality of parallel-connected small inverters.
A plurality of parallel-connected small inverters may configure a large inverter. For this purpose, the parallel-connected inverters have to be driven where each of PWM carriers must be in synchronization. However, when a noise occurs in a PWM synchronization signal, the noise itself is recognized as a synchronization signal, and consequently, a corresponding PWM carrier is turned into ‘0’. This phenomenon causes irregular changes in the PWM carrier, which has been known as a technical problem in the conventional art.
In addition, when a PWM carrier is forcibly turned into ‘0’, an output of the inverter trembles to generate another known technical problem in the conventional art.
[Reference 1] Korea Patent Registration No. 10-1304055 (published on 2013 Sep. 4)
[Reference 2] Japan Patent Publication No. 2010-288420 (published on 2010 Dec. 24)